A laser beam apparatus such as an OBIRCH (Optical Beam Induced Resistance Change) measuring apparatus as disclosed in JP-A-2001-4719, for example, is known as an apparatus for inspecting an inner defect in a sample such as semiconductor integrated circuits. The OBIRCH measuring equipment irradiates a laser beam to the sample, and measures a change in the value of resistance within the simple caused by the heat generation accompanied by beam heat. FIG. 1 is a block diagram showing a construction of conventional OBIRCH measuring equipment as the laser beam inspection apparatus. As shown in FIG. 1, in the conventional OBIRCH measuring equipment 60, upon the optical 20, path of a laser beam emitted from a laser source 61, a laser scanning unit 62 for raster-scanning the laser beam in a two-dimensional direction perpendicular to its incident direction, and a microscope 63 for condensing the scanned laser beam L at a micro-spot diameter are arranged. A sample T such as semiconductor integrated circuits is disposed on a sample base 64 at a focus point of the microscope 63. A predetermined voltage is applied to the sample T from a constant voltage supply 65. The sample T is connected to a current/voltage converter including an operational amplifier, a feedback resistor, and the like. The current/voltage converter 66 is connected to a system controller 67, and the system controller 67 further is connected to a monitor 68. The system controller 67 is also connected to a laser scanning unit 62. Furthermore, the system controller 67 is connected to a temperature controller 69 for maintaining the temperature of the sample base 64 at a predetermined temperature.
The laser beam L emitted from the laser source 61 is raster-scanned in a two-dimensional direction that is perpendicular on the optical path by means of the laser scanning unit 62, and further condensed by the microscope 63 to be irradiated to a fine area on the surface of the sample T. This laser beam scanning is controlled by the system controller 67. A given voltage is applied in advance to the sample T by the constant voltage supply 65, and a given current is flown in the circuit. At the irradiation spot of the sample T irradiated by the laser beam, the temperature of the spot rises with absorption of the laser beam and thereby the specific resistance thereof changes. Therefore, the amount of current flown in the sample T also changes. The heat conductance is poor at the position having voids and so on. For this reason, when the laser beam is irradiated to such a position, it is hard to escape generated heat at the ambience, resulting in a great temperature rise. Consequently, at the defective spot of the sample applied by the given voltage, the change in the specific resistance is increased with an increase of the temperature, and the change of the value of current is also enlarged.
In the current/voltage converter 66, the detected current is converted to a voltage after it is once amplified, and a detection signal corresponding to the converted voltage value is transferred from the current/voltage converter 66 to the system controller 67. The system controller 67 converts the difference of the voltage values each obtained as a detection signal to brightness information, and displays lined up image information corresponding to laser beam irradiation positions on the monitor 68. In this way, the defective spot of the sample T may be confirmed by an image.